Self-trimming sailset

ABSTRACT

A principal sail (1) rotates about an erect axis (2) and an auxiliary sail or vane (3) is mounted downstream of the principal sail (1). The vane (3) is mounted on a boom (4) that extends from the principal sail (1) so that the principal sail (1) is trimmed as the tail vane (3) moves to its position of minimum drag. A second auxiliary vane (5) is mounted forwards of the leading edge of the principal sail (1) and is capable of opposing the moment of the principal sail (1) about its own axis as the principal sail is moved towards a stalling position.

This invention relates to sails for marine or terrestrial vessels, andespecially to self-trimming sailsets.

A known type of self-trimming sailset consists of a principal sail thatis rotatable about an erect axis and an auxiliary sail or "tail vane"that is carried downstream of the principal sail. This tail vane ismounted on a boom that extends from the principal sail so that thrust onthe tail vane rotates the tail vane and boom about the erect axis andcauses rotation of the principal sail. In operation, the angle of thetail vane, with respect to the principal sail, is set, the resultingthrust of the wind on the tail vane urging the tail vane and boomtowards the position of minimum drag for the tail vane and thus causingrotation of the principal sail to an angle of attack predetermined bythe setting of the tail vane.

These self-trimming sailsets have advantages over conventional sailingrigs in terms of controllability, efficiency and drive, but tend tosuffer from relatively poor downwind performance due to the inability ofthe tail vane to stall fully the principal sail.

The present invention is directed towards alleviating the aforesaiddisadvantage of self-trimming sailsets.

According to one aspect of the invention there is provided aself-trimming sailset including an auxiliary vane capable of beingpositioned forwards (i.e. usually upwind) of the leading edge of theprincipal sail and such that thrust on the auxiliary vane causesrotation of the principal sail.

Another aspect of the invention provides a self-trimming sailsetincluding at least one auxiliary vane that is capable of opposing themoment of the principal sail about its own axis as the principal sail ismoved towards a stalling position.

The auxiliary vane is preferably rigid, most preferably a rigid aerofoilof symmetrical section that is pivoted ahead of its centre of pressure.

The sailset preferably comprises counterbalancing weights which may beincorporated into the auxiliary vane or be carried by a boom on whichthe auxiliary vane is mounted.

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a schematic plan view of a self-trimming sailset in accordancewith an embodiment of the invention;

FIG. 2 is an enlarged schematic plan view of the auxiliary sails of thesailset of FIG. 1;

FIGS. 3 and 4 show, respectively, in schematic plan view, theconfiguration of the sailset of FIG. 1 adopted for port and starboardtacking;

FIGS. 5 and 6 show in schematic plan view the sailset of FIG. 1 in theconfiguration adopted for port and starboard stalling; and

FIG. 7 shows a side view of the sailset of FIG. 1.

Referring to FIG. 1, there is a principal sail 1, shown as a symmetricalsection aerofoil, which is freely rotatable about an erect axis 2, and atail vane 3 mounted on a boom 4 that extends from the principal sail 1.In addition to the tail vane 3 there is a second auxiliary vane that innon-stalling conditions is positioned upwind of the principal sail. Thissecond auxiliary vane, referred to herein as forward vane 5, alsoextends on a boom 7 from the principal sail 1.

The axis 2 of the principal sail 1 is positioned on the chord of theaerofoil section at a distance from the leading edge of the aerofoilthat is within the zone in which the centre of pressure of the aerofoilgenerally occurs in non-stalled modes of operation. This zone willgenerally lie in the range from 22% to 40% of the chord length measuredfrom the leading edge. The tail vane 3 is also pivoted about an erectaxis preferably within the zone in which its centre of pressuregenerally occurs. The forward vane 5 is freely pivoted about an erectaxis 6 the location of which is upstream of the zone in which its centreof pressure generally occurs, preferably in the range of 0% to 18% ofthe chord length measured from the leading edge although the forwardvane 5 may be pivoted about an axis disposed forwards of its leadingedge.

FIG. 2 shows an enlarged view of the extremities of the booms 4 and 7carrying respectively the tail vane 3 and forward vane 5, from which itcan be seen that the trailing edge of the forward vane 5 is linked tothe tail vane by a rope 12. The rope 12 passes through guides 11, suchas sheaves, and at the tail vane 3 is attached to an extension 13 thatprojects forwards of the tail vane. The length of the rope 12 is suchthat it remains slack as the tail vane 3 is moved between its normaloperating positions (that is positions in which the principal sail isnot stalled) by means of arms 10, a typical arrangement allowing therope 12 to remain slack while the tail vane is deviated by up to atleast 30° in either direction. When rope 12 is slack the forward vane 5is able to align itself to the local air flow in a "weathercocking"fashion, but when rope 12 is pulled taut by deviating the tail vane 3beyond its normal range of operating positions the forward vane 5 ispulled towards alignment with the boom 7 and held so that thrust of thewind on the forward vane 5 causes the forward vane to move on its boomabout the axis 2 of the principal sail, and thus alter the alignment ofthe principal sail with respect to the wind.

FIGS. 3 and 4 illustrate the general conditions for, respectively,unstalled port and starboard tacking. In these Figures flow lines 14indicate the airflow, and it can be seen that, in each case, theprincipal sail 1 is positioned at the desired angle of attack by thesetting of the tail vane 3 which is urged towards its position ofminimum drag, the rotation of the boom 4 as the tail vane 3 takes upthis position having served to rotate the principal sail 1. Thus in thisembodiment the tail vane 3 acts as a regulator which, once set, rendersthe sailset self-trimming. The setting of the tail vane 3 is such thatrope 12 is slack and therefore the forward vane 5 "weathercocks" toalign with the local air flow by virtue of being pivoted ahead of itscentre of pressure.

FIGS. 5 and 6 show respectively the sailset configuration that isnecessary for port and starboard stalling, as may be required whensailing downwind. As shown, the tail vane 3 has been deviated to theextreme angle of about 90°, thus pulling the rope 12 taut and aligningthe forward vane 5 with the boom 7. With the forward vane 5 so fixed,the thrust of the wind tends to turn the forward vane 5 on its boom 7about the axis 2 of the principal sail 1 until both the principal sailand forward vane stall as depicted in FIGS. 5 and 6; flow lines 16represent the fully stalled eddying flow of air about the stalledaerofoils.

The precise extent to which the tail vane 3 must be deviated to make therope 12 taut depends on the length of the rope and the relative lengthof other members such as the extensions 13. As shown the tail vane isaligned with the wind direction and the forward vane is aligned with itsboom, however it is merely necessary for the helmsman to deviate thetail vane through the maximum angle that the rope permits, which in analternative embodiment need not fully align (or centralise) the forwardvane with respect to its boom.

In the above description, the axis 2 of the principal sail 1 has beendescribed as in the zone in which the centre of pressure of theprincipal sail generally occurs. However, as the principal sail isrotated towards an angle of attack of 90°, in order to achieve stalling,the centre of pressure moves along the chord, away from the leadingedge, until eventually there is a significant moment about the axis 2due to thrust on the principal sail 1 itself, acting to oppose rotationinto a stalling position. Thus it may be seen that the forward vane 5acts to oppose the moment of the principal sail 1 about its own axis asthe principal sail is moved to the stalling position. Under theseconditions an equilibrium is eventually reached where the moment of theforward vane equals the moment of the principal sail, about axis 2. Thearea of the forward vane is chosen so as to cause a net angle of attacksubstantially greater than that corresponding to stalling conditions.

FIG. 7 illustrates a side view of a sailset similar to that shown inFIGS. 1 to 6.

In FIGS. 1 to 7 the principal sail 1 and the auxiliary sails, i.e. tailvane 3 and forward vane 5, are shown as single rigid symmetricalaerofoils, however each may be a cloth sail and/or may be amulti-element sail, and in the case of the auxiliary sails beingmulti-element they may be mounted on one or a plurality of booms. Alsowhile symmetry about the axis A--A, shown in FIG. 1, is preferable it isnot essential.

In a preferred embodiment, the boom (or booms) 7 or the forward vane (orvanes) 5 carry balance weights for counterbalancing the sailset aboutthe principal sail axis 2, for example as shown by weights 17 and 18 inFIG. 7. Alternatively the weights may be constituted by a bar extendingfrom the boom or booms, the forward vane being pivoted upon the bar. Theboom 7, in addition to rotating about axis 2 may be pivoted to theprincipal sail 1 near its leading edge to allow rotation of the boom 7for relocation of the balance weights without causing rotation of theprincipal sail. In this instance the pivoting action of the boom aboutthe leading edge of the principal sail 1 is inhibited by some means,such as a locking device, when it is desired to use the forward vane torotate the principal sail.

The loci of the forward vane 5 and tail vane 3, shown as circle 8 inFIG. 1 where the loci coincide as the leading edge of the forward vaneand the trailing edge of the tail vane are equidistant from axis 2,preferably lie within the plan outline of the vessel so as to minimisethe danger of accidental fouling of the sailset. (FIGS. 3 to 6, forsimplicity, depict a smaller vessel outline). In order to reduce themoment of inertia of the sailset it is preferable to have the leadingedge of the forward vane 5 closer to the axis 2 than the trailing edgeof the tail vane 3.

It is envisaged that the rope 12 for fixing the forward vane 5 could bereplaced by other linkages such as push rods or bell cranks, or evenreplaced by a servo mechanism. Furthermore, it is not essential that theforward vane, when operating to rotate the principal sail, be fixed inparallel alignment with the boom, as shown in the Figures, for examplethe or each forward vane may be mounted off centre with respect to itsboom.

Alternative arrangements for fixing the forward vane, other than bymaximum deflection of the control for the tail vane, are envisaged. Forexample flaps on the principal sail may be linked to the forward vane,or there may be a linkage only from the forward vane to its boom. If thecontrol of the forward vane is to be manual it is desirable that theoperation consist of movement of a control member to an extremeposition, such as the described movement of the control for the tailvane, or movement of the forward vane boom to an extreme position.

The forward vane may also constitute a fairing for the counterbalancingweights.

I claim:
 1. A self-trimming sail set comprising:an upright principalsail mounted freely for rotation about an upright axis; a tail vanesettable for controlling the angle of attack of the principal sail tothe wind; an auxiliary vane mounted in a position normally upstream ofthe principal sail; and control means for setting the auxiliary vane tooppose the moment of the principal sail about its said axis when thetail vane is set to cause the principal sail to move towards a stalledcondition, said control means being operable to allow said auxiliaryvane to weathercock when said tail vane is set for a normal non-stallingcondition of said principal sail.
 2. In a self-trimming sailsetincluding a principal rigid aerofoil sail mounted freely for rotationabout an upright axis and a rigid control aerofoil for controlling theangle of attack of the principal sail to the wind, the control aerofoilbeing settable to cause the principal sail to rotate towards a stalledcondition such that the center of pressure of said principal sail shiftsto produce a moment opposing the rotation of the principal sail towardssaid stalled condition, apparatus for opposing said moment and assistingthe principal sail to achieve a fully stalled condition, said apparatuscomprising:an upright auxiliary rigid aerofoil, said auxiliary aerofoilbeing mounted for rotation about an upright axis positioned ahead of thecenter of pressure of said auxiliary aerofoil, whereby said auxiliaryaerofoil cna weathercock; and means for setting said auxiliary aerofoilat a selected angle such that wind thrust on said auxiliary aerofoilopposes said moment.
 3. A self-trimming sailset comprising:an uprightrigid principal aerofoil freely mounted for rotation about an uprightaxis; an upright rigid control aerofoil pivoted for movement about anupright axis, said control aerofoil controlling the angle of attack ofsaid principal aerofoil to the wind; an upright rigid auxiliary vanepivoted about an upright axis forwardly of its center of pressure, saidauxiliary vane being positionable forwards of said principal aerofoil;and control means for linking said control aerofoil and said auxiliaryvane, said control means permitting said auxiliary vane to weathercockwhen said control aerofoil is set for non-stalling operation of saidprincipal aerofoil and setting said auxiliary vane to a selected anglewhen said control aerofoil is set to cause said principal aerofoil tomove to a stalled position.
 4. A sailset according to claim 3 whereinsaid selected angle is such that the auxiliary vane is aligned with saidprincipal aerofoil.